We consider the problem of estimating the frame error rate (FER) of a given memoryless binary symmetric channel by observing the success or failure of transmitted packets. Whereas FER estimation is relatively straightforward if all observations correspond to packets with equal length, the problem becomes considerably more complex when this is not the case. We develop FER estimators whentransmissions of different lengths are observed, together with the Cramer-Rao Lower Bound (CRLB). Although the main focus is on Maximum Likelihood (ML) estimation, we also obtain low complexity schemes performing close to optimal in some scenarios. In a second stage, we consider the case in which FER estimation is performed at a node different from the receiver, and incorporate the impairment of unreliable observations by considering noisy ACK/NAK feedback links. The impact of unreliable feedback is analyzed by means of the corresponding CRLB. In this setting, the ML estimator is obtained by applying the Expectation-Maximization algorithm to jointly estimate the error probabilities of the data and feedback links. Simulation results illustrate the benefits of the proposed estimators.

GPSC is funded by the Agencia Estatal de Investigación (Spain) and the European Regional Development Fund (ERDF) under projects COMPASS (TEC2013-47020-C2-1-R), WINTER (TEC2016-76409-C2-2-R), MYRADA (TEC2016-75103-C2-2-R), COMONSENS (TEC2015-69648-REDC). Also funded by the Xunta de Galicia and the European Union (European Regional Development Fund - ERDF) under projects Agrupación Estratéxica Consolidada de Galicia accreditation 2016-2019 and Red Temática RedTEIC 2017-2018. Also funded by the EU H2020 Programme under project WITDOM (project no. 644371).